Translation Elongation Factor EF-P Alleviates Ribosome Stalling at Polyproline Stretches

Translating Polyproline Translation of messenger RNA into protein is carried out by the ribosome, together with a variety of accessory factors, which offer the potential for regulation of this critical step in gene expression (see the Perspective by Buskirk and Green). Ude et al. (p. 82, published online 13 December), using bacterial genetics and an in vitro reconstituted translation system, and Doerfel et al. (p. 85, published online 13 December), using a model assay for peptide bond formation, find that the universally conserved bacterial elongation factor P (EF-P) (which is orthologous to the archaeal and eukaryotic initiation factor 5A) is required for the efficient translation of polyproline-containing polypeptides. Such short polyproline stretches (with runs of two, three, or more proline residues) would otherwise cause ribosomal stalling. A universally conserved translation factor facilitates synthesis of peptides that would otherwise cause ribosome stalling. [Also see Perspective by Buskirk and Green] Translation elongation factor P (EF-P) is critical for virulence in bacteria. EF-P is present in all bacteria and orthologous to archaeal and eukaryotic initiation factor 5A, yet the biological function has so far remained enigmatic. Here, we demonstrate that EF-P is an elongation factor that enhances translation of polyproline-containing proteins: In the absence of EF-P, ribosomes stall at polyproline stretches, whereas the presence of EF-P alleviates the translational stalling. Moreover, we demonstrate the physiological relevance of EF-P to fine-tune the expression of the polyproline-containing pH receptor CadC to levels necessary for an appropriate stress response. Bacterial, archaeal, and eukaryotic cells have hundreds to thousands of polyproline-containing proteins of diverse function, suggesting that EF-P and a/eIF-5A are critical for copy-number adjustment of multiple pathways across all kingdoms of life.